This project seeks to develop new statistical methodologies for problems in human development and to apply existing methodologies to those problems in novel ways. Work continues in two areas: (1) statistical modeling of the distribution of birthweights in human populations, and (2) statistical modeling of developmental trajectories of reproductive hormones in children through puberty. Development of a satisfactory statistical model for the distribution of birthweights in a population will facilitate a refined understanding of the relationship of birthweight to infant mortality. Having developed a model and a method for fitting the model to data that allow us to measure selected features of birthweight distributions, we are applying our technique to U.S. birthweight and perinatal mortality data to assess how well mortality rates are predicted by features of birthweight distributions that our technique measures. Serum levels of gonadotropins and gonadal hormones change as children develop through puberty. We have developed parsimonious descriptions of hormonal development through puberty by fitting certain nonlinear regression models to the logarithm of hormone level as a function of either testis volume or Tanner stage and have compared developmental trajectories of FSH, LH, and inhibin between boys and girls. Boys exhibit a steep rise in log LH early in puberty whereas in girls this early rise is more gradual.